[PATCH 07/10 v3] libdw: Make libdw_find_split_unit thread-safe

[Aaron Merey]

From: Heather McIntyre <h...@rice.edu>

        * libdw/libdwP.h (struct Dwarf_CU): Add split_lock.
        * libdw/libdw_find_split_unit.c (__libdw_find_split_unit):
          Add locking.

Signed-off-by: Heather S. McIntyre <h...@rice.edu>
Signed-off-by: Aaron Merey <ame...@redhat.com>
Signed-off-by: Mark Wielaard <m...@klomp.org>

---
v3 changes:
Move Dwarf split_lock code from patch 3/9 v2 to this patch.
Assign return value before releasing lock.

 libdw/dwarf_end.c             |  1 +
 libdw/libdwP.h                |  3 +++
 libdw/libdw_find_split_unit.c | 15 +++++++++++++--
 libdw/libdw_findcu.c          |  1 +
 4 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/libdw/dwarf_end.c b/libdw/dwarf_end.c
index 487d6ce7..ee3ed74e 100644
--- a/libdw/dwarf_end.c
+++ b/libdw/dwarf_end.c
@@ -69,6 +69,7 @@ cu_free (void *arg)
     {
       Dwarf_Abbrev_Hash_free (&p->abbrev_hash);
       rwlock_fini (p->abbrev_lock);
+      rwlock_fini (p->split_lock);
 
       /* Free split dwarf one way (from skeleton to split).  */
       if (p->unit_type == DW_UT_skeleton
diff --git a/libdw/libdwP.h b/libdw/libdwP.h
index 48c34871..8f942433 100644
--- a/libdw/libdwP.h
+++ b/libdw/libdwP.h
@@ -454,6 +454,9 @@ struct Dwarf_CU
   /* Synchronize Dwarf_Die abbrev access.  */
   rwlock_define(, abbrev_lock);
 
+  /* Synchronize split Dwarf access.  */
+  rwlock_define(, split_lock);
+
   /* Memory boundaries of this CU.  */
   void *startp;
   void *endp;
diff --git a/libdw/libdw_find_split_unit.c b/libdw/libdw_find_split_unit.c
index 4005793b..f4f34c5d 100644
--- a/libdw/libdw_find_split_unit.c
+++ b/libdw/libdw_find_split_unit.c
@@ -150,9 +150,18 @@ Dwarf_CU *
 internal_function
 __libdw_find_split_unit (Dwarf_CU *cu)
 {
+  /* Set result before releasing the lock.  */
+  Dwarf_CU *result;
+
+  rwlock_wrlock(cu->split_lock);
+
   /* Only try once.  */
   if (cu->split != (Dwarf_CU *) -1)
-    return cu->split;
+    {
+      result = cu->split;
+      rwlock_unlock(cu->split_lock);
+      return result;
+    }
 
   /* We need a skeleton unit with a comp_dir and [GNU_]dwo_name attributes.
      The split unit will be the first in the dwo file and should have the
@@ -207,5 +216,7 @@ __libdw_find_split_unit (Dwarf_CU *cu)
   if (cu->split == (Dwarf_CU *) -1)
     cu->split = NULL;
 
-  return cu->split;
+  result = cu->split;
+  rwlock_unlock(cu->split_lock);
+  return result;
 }
diff --git a/libdw/libdw_findcu.c b/libdw/libdw_findcu.c
index 0f46d777..c74e895e 100644
--- a/libdw/libdw_findcu.c
+++ b/libdw/libdw_findcu.c
@@ -178,6 +178,7 @@ __libdw_intern_next_unit (Dwarf *dbg, bool debug_types)
   newp->endp = data->d_buf + newp->end;
   eu_search_tree_init (&newp->locs_tree);
   rwlock_init (newp->abbrev_lock);
+  rwlock_init (newp->split_lock);
 
   /* v4 debug type units have version == 4 and unit_type == DW_UT_type.  */
   if (debug_types)
-- 
2.45.2